Genetic engineering has allowed the improvement of microorganisms used as industrial bioreactors, cell factories and in food fermentations. In particular, filamentous fungi (e.g. Aspergillus and Trichoderma species) and certain bacteria (e.g., Bacillus species) produce and secrete a large number of useful proteins and metabolites (Bio/Technol. 5: 369-376, 713-719 and 1301-1304 [1987] and Zukowski, “Production of commercially valuable products,” In: Doi and McGlouglin (eds.) Biology of Bacilli: Applications to Industry, Butterworth-Heinemann, Stoneham. Mass pp 311-337 [1992]). Important production enzymes include glucoamylases, α-amylases, cellulases, neutral proteases, and alkaline (or serine) proteases, and important production proteins include hormones and antibodies. However, the occurrence of protein degradation and modification in some of these host cells provides a major hurdle for protein production, and in spite of advances in the understanding of production of proteins in filamentous fungal host cells, there remains a need for methods to increase expression of important proteins.
Accordingly, an object of the present invention is to provide an Aspergillus strain defective in protein degrading genes and protein modification genes, which can be used for more efficient production of heterologous or homologous proteins of interest.